1. Field of the Invention
The present invention relates to a load cell weighing apparatus, the weighing range of which is selectable.
2. Description of the Related Art
Published Unexamined Japanese patent application (PUJPA) No. 56-154618 discloses a conventional load cell weighing apparatus. The load cell weighing apparatus comprises a load cell for generating an output voltage according to a load weight, an amplifier for amplifying the output voltage from the load cell, and an A/D converter for converting the amplified analog output voltage to digital data. The load cell weighing apparatus further comprises an attenuator to select the weighing range. The output voltage of the amplifier is supplied to the A/D converter without passing though the attenuator when a light weight range is selected, and is supplied to the A/D converter through the attenuator when a heavy weight range is selected. This attenuator causes the output voltage of the amplifier to be attenuated by a predetermined degree. The output of the A/D converter is converted to the weight data to be displayed on a scale corresponding to a selected weighing range.
Since the attenuator decreases a variation in input voltage to the A/D converter corresponding to a variation in the load weight, a heavy load can be weighed without increasing an allowable input voltage of the A/D. However the weighing sensitivity in a heavy weight range becomes lower than that in a light weight range.